Wastewater Overflow: What, When, and Where does this happen?

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For the most part, my experience with the river has been a clean one. The river can be a very safe and enjoyable place to swim given the point of entry and under the right conditions. In this blog I’d like to point out certain spots around the river to be aware of when choosing where to go in, as well as to inform people on when our sewage and stormwater may be entering the river.

Sewage and wastewater in Edmonton go to the Gold Bar Water Treatment Plant where it is treated and cleaned before entering back into the river. However, on periods of heavy rainfall or snowmelt some of the main trunks cannot handle all of the excess water, resulting in an overflow which sends raw wastewater into the river. This mostly happens in older city neighborhoods due to the combined sewer system where stormwater and sewage run on the same line.

When these pipes “overflow” the wastewater is sent to Combined Sewer Overflows (CSO). There are 18 CSO’s stationed along the river, starting at the Walterdale Bridge and ending at Hermitage Park. Some of these overflows are more active than others leading to greater discharge volumes in those locations. Below are the names of each CSO in order of highest to lowest discharge volume and number of days of overflow from 2017. Volume is measured in cubic metres (m3) – 1 m3 is about the size of a washing machine.

Gold Bar Treatment Plant 1 – 4,233,900 m3 over 79 days

Rat Creek – 437,239 m3 over 31 days

Highlands & Beverly 1 – 24,097 m3 over 6 days

Calder 1 (Hermitage Park) – 13,785 m3 over 36 days

Gold Bar Treatment Plant 2 –  2,540 m3 over 5 days

Strathearn 1 & 2 – 527 m3 over 1 day

Calder 2 –  46 m3 over 2 days

Cromdale – 26 m3 over 1 day

The other 10 CSO’s did not have any overflows in 2017, meaning no raw wastewater was released at these locations.

Recently, Epcor completed a new tunnel system under the river as well as sewer gates to hold more water and limit overflows during heavy precipitation events. This is intended to reduce the amount of raw wastewater entering the river. The project was completed last fall so it will be interesting to see if the amount of discharge volume will be significantly less this year compared to previous years, of course taking into account that years differ depending on amount of rainfall and snowmelt as well. Below is a table comparing 2016 and 2017 total discharge volume.

As shown above there was more overflow discharge in 2016 then there was in 2017. A total of 5,724,439m3 of wastewater was discharged in 2016 and a total of 4,712,160m3 was discharged in 2017. Hopefully with the new tunnel system in place the volume amount will be less in 2018.

The Edmonton Journal recently released an article about sewage displacement in the river. They provide an interactive map showing where all the CSO locations are in Edmonton as well as data from those locations over the last 5 years. Be encouraged to check out these locations and the data history to have a better idea of where it may be good to swim/interact with the river.

Precipitation is the leading cause to poor water quality because it can cause overflow and wastewater to runoff into the river. Remember the 48 hour rule – swimming should be avoided 48 hours after a significant rain event.

We encourage people to enjoy and appreciate the North Saskatchewan River. When doing so it’s important to take precaution and to be aware of potential hazards when planning your next excursion.


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